基于MODPATH模型的单井抽出-回渗循环地下水水力控制程度的关键影响因素研究

Study of Key Influencing Factors on the Degree of Hydraulic Control of Groundwater in Single-Well Pumping-Percolation Cycle Based on the MODPATH Model

为研究单井抽出-回渗循环地下水水力控制程度(抽水井对回渗水的捕获率)和关键因素对水力控制程度的影响机制,构建了基于GMS模拟软件的MODPATH地下水流线示踪模型,根据实验室尺度砂柱物理模型的实测水位数据校准,结合渗透系数为0.009、0.02、0.04、0.09 cm/s四种不同水文地质条件和抽出回渗量为1、2.5、5、10 cm^(3)/s四种水动力条件以及25、30、32、35 cm四种回渗半径的情景设置,模拟了地下水质点的迁移轨迹,刻画了抽水井的捕获范围,量化了抽水井对地下水流场的水力控制程度,并构建了水力控制程度与关键参数之间的定量关系.结果表明:①砂柱物理模型在1、2.5、5、10 cm^(3)/s四种流量下达到抽出-回渗平衡时,捕获率分别为95.63%、97.69%、97.93%和98.17%;②物理模型内抽水井捕获范围均小于回渗范围且捕获率随流量增加而变大;③回渗范围和含水层渗透系数一定时,随着抽出-回渗量的增大,捕获范围和捕获率均增大;④当回渗范围和抽出-回渗量一定时,随着含水层渗透系数的增大,捕获范围和捕获率均减小;⑤当含水层渗透系数和抽出-回渗量一定时,随着回渗范围的增大,捕获范围和捕获率均减小;⑥根据64种情景的拟合结果,水力控制程度与含水层渗透性强弱、抽出-回渗量大小和回渗半径之间存在定量关系——η=100%×[0.9ln(Q/K)−0.4R+10^(4)]〔η为水力控制程度(%),Q为抽出-回渗量,K为含水层渗透系数,R为回渗半径〕.研究显示,单井抽出-回渗循环地下水水力控制程度与抽出-回渗量、含水层渗透系数和回渗范围间存在对应关系,可以有效指导实际场地工程应用中实现水力控制的关键参数的设计.

In order to study the degree of hydraulic control of groundwater(the capture rate of back seepage water by the pumping well)in single-well pumping-percolation cycle and the influence mechanism of key factors on the degree of hydraulic control,a MODPATH groundwater flowline tracer model based on GMS simulation software was constructed.Based on the measured water level data of the laboratory-scale sand column physical model,combined with four different permeability coefficients of 0.009,0.02,0.04 and 0.09 cm/s hydrogeological conditions and four hydrodynamic conditions of 1,2.5,5 and 10 cm3/s of pumping back seepage and four scenarios of 25,30,32 and 35 cm of back seepage radius,the migration trajectory of groundwater masses was simulated,the capture range of pumping wells was portrayed,the degree of hydraulic control of groundwater flow field by pumping wells was quantified,and the quantitative relationship between the degree of hydraulic control and key parameters was constructed.The results show that:(1)When the physical model of sand column reaches the pumping and percolation equilibrium flow rate of 1,2.5,5 and 10 cm3/s,the capture rate is 95.63%,97.69%,97.93%and 98.17%,respectively.(2)The capture range of pumping wells in the physical model is smaller than the percolation range and the capture rate becomes larger with increasing flow rate.(3)When the re-infiltration range and aquifer permeability coefficient are fixed,both the capture range and capture rate increase with the increase of pumping-out-infiltration volume.(4)When the re-infiltration range and pumping-out-infiltration volume are fixed,both the capture range and capture rate decrease with the increase of aquifer permeability coefficient.(5)When the aquifer permeability coefficient and pumping-out-infiltration volume are fixed,both the capture range and capture rate decrease with the increase of re-infiltration range.(6)According to the fitting results of 64 scenarios,the degree of hydraulic control is related to the aquifer according to the fitting results of 64 scenarios.There is a quantitative relationship between the degree of hydraulic control and aquifer permeability strength,the size of pump-out-return seepage volume and retrieval radiusη=100%×[0.9ln(Q/K)−0.4R+104](ηis the degree of hydraulic control(%),Q is the pump-out-return seepage volume,K is the aquifer permeability coefficient,and R is the retrieval radius).This study shows that there is a correspondence between the degree of hydraulic control of groundwater in single-well pumping-percolation cycle and the pumping-percolation volume,aquifer permeability coefficient,and percolation range,which can effectively guide the design of key parameters for achieving hydraulic control in field applications.